Optical Instrumentation for Chromospheric Monitoring During Solar Cycle 25 at Paris and Cфte D'azur Observatories

J. Space Weather Space Clim. 2020, 10,31 Ó J.-M. Malherbe et al., Published by EDP Sciences 2020 https://doi.org/10.1051/swsc/2020032 Available online at: www.swsc-journal.org Topical Issue - Space Weather Instrumentation TECHNICAL ARTICLE OPEN ACCESS Optical instrumentation for chromospheric monitoring during solar cycle 25 at Paris and Coˆ te d’Azur observatories Jean-Marie Malherbe1,*, Thierry Corbard2, and Kevin Dalmasse3 1 LESIA, Observatoire de Paris, PSL Research University, CNRS, 92195 Meudon, France 2 Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 06304 Nice, France 3 IRAP, Université de Toulouse, CNRS, CNES, UPS, 31028 Toulouse, France Received 8 April 2020 / Accepted 21 June 2020 Abstract – We present the observing program proposed by Paris and Côte d’Azur Observatories for monitoring solar activity during the upcoming cycle 25 and providing near real time images and movies of the chromosphere for space-weather research and applications. Two optical instruments are fully dedicated to this task and we summarize their capabilities. Short-term and fast-cadence observations of the chromosphere will be performed automatically at Calern observatory (Côte d’Azur), where dynamic events, as flare development, Moreton waves, filament instabilities and Coronal Mass Ejections onset, will be tracked. This new set of telescopes will operate in 2021 with narrow bandpass filters selecting Ha and CaII K lines. We present the instrumental design and a simulation of future images. At Meudon, the Spectroheliograph is well adapted to the long-term and low-cadence survey of chromospheric activity by recently improved and optimized spectroscopic means. Surface scans deliver daily (x, y, k) datacubes of Ha, CaII K and CaII H line profiles. We describe the nature of available data and emphasize the new calibration method of spectra. Keywords: Sun / chromosphere / optical observations / solar cycle 25 1 Introduction coronographs (SoHO/LASCO, ESA/NASA, since 1996; STEREO/NASA since 2006). Parker Solar Probe (NASA, Solar activity is the primary driver of space weather and launched in 2018) observes in situ the far corona and the Solar space climate (e.g., Schrijver et al., 2012; Pomoell & Poedts, Orbiter mission (ESA) started early 2020. SDO/HMI provides 2018). It varies over a wide range of time scales from several in addition photospheric magnetograms and dopplergrams. minutes with solar flares and Coronal Mass Ejections (CMEs; We summarize below the interest of chromospheric obser- e.g., Shibata & Magara, 2011) to hundreds of years with the vations in the scope of space weather research and applications. 100-year modulation (Gleissberg cycle) of the 11-year solar Then we review the state of instrumentation dedicated to this cycle (e.g., Hathaway, 2015). Both short-term and long-term task at Paris (OP) and Côte d’Azur (OCA) observatories in full-disk observations of the Sun are thus critical for improving the context of the upcoming solar cycle 25. Section 2 presents our understanding of solar activity at all time scales, but also for new instrumentation for short-term, high-cadence monitoring monitoring and predicting it in space weather forecast applica- of solar activity. The widely open data will be used by the tions (e.g., Ueno et al., 2010; Malherbe et al., 2019). french Air Force for space weather forecast and by the scientific Ground-based observations of the chromosphere are of community to investigate unstable phenomena as flares, particular interest, because this layer is the source of solar Moreton waves or CMEs. Section 3 describes the long-term, activity. Two international networks are already operating with low-cadence Spectroheliograph while Section 4 develops the several ground-based stations at various longitudes: the Global wavelength calibration of new datacubes. Ha Network (GHN, http://ghn.njit.edu) and the GONG Ha network (http://halpha.nso.edu). Counterparts in the hot corona above are observed in EUV by Solar Dynamics Observatory 1.1 Short-term, high-cadence chromospheric (SDO/AIA, NASA, since 2010) or radiotelescopes (e.g., observations Nançay, Nobeyama). Events at large distance of the Sun (up a to 30 rad) are tracked by several wide angle, white light space High-cadence H observations are widely used in the context of solar flare/CME analyses and monitoring (e.g., Deng *Corresponding author: [email protected] et al., 2002; Huang et al., 2014). In the case of filament This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. J.-M. Malherbe et al.: J. Space Weather Space Clim. 2020, 10,31 eruptions, such data allow one to follow the pre-, and early-, properties of the solar cycle and its cycle-to-cycle variability. It eruptive dynamics of the filament, which provide insights into can introduce an activity asymmetry and time lag between the both the CME triggering and driving mechanisms when com- North and South solar hemispheres (similar to the one already bined with the analysis of other datasets such as photospheric observed; e.g., McIntosh et al., 2013; Svalgaard & Kamide, magnetic field data (e.g., Joshi et al., 2014; Chen et al., 2013), or trigger a grand minimum in the subsequent cycles 2018). Adopting the framework of the Torus Instability (one (similar to the Maunder minimum; e.g., Spoerer & Maunder, of the main models considered for CME trigger/driver; Kliem 1890; Ribes & Nesme-Ribes, 1993). & Török, 2006; Démoulin & Aulanier, 2010), then Ha imaging CaII K3 (line center) and Ha imaging can also be used to can further be used to monitor the slow rise of the filament and probe the magnetic properties of solar active regions and the predict when it will reach the critical height for the onset of the energy of solar flares in old archives, both of which are essential instability (e.g., Filippov & Zagnetko, 2008; McCauley et al., to research on extreme solar flares for the development of 2015). space weather prediction tools (e.g., Gopalswamy, 2017; Tsiftsi More generally, high-cadence Ha observations are further &DelaLuz,2018). For instance, CaII K spectroheliograms interesting because they also register the chromospheric response provide a means to estimate the magnetic flux in plages to solar flares/CMEs, as flare ribbons (e.g., Wang et al., 2003; and sunspots, thus enabling the construction of pseudo- Jiang et al., 2014)andMoretonwaves(e.g.,Narukage et al., magnetograms (e.g., Harvey & White, 1999; Pevtsov et al., 2008; Muhr et al., 2010). Flare ribbons are “surface” brighten- 2016). Using empirical laws derived from observations and ings (often observed in EUV and Ha) caused by the interaction MHD models, one can further quantify the flare-energy release of energetic particles and thermal energy (emitted at the coronal from Ha bright ribbons (e.g., Toriumi et al., 2017), and/or the reconnection region) with the lower and denser layers of the maximum energy available for a solar flare from the CaII K size solar atmosphere (e.g., Schmieder et al., 1987; Fletcher et al., and area of an active region (e.g., Aulanier et al., 2013). 2011). Moreton waves are large-scale disturbances that appear as arc-shaped, bright fronts in the center and blue wing of the Ha line (e.g., Moreton, 1960; Zhang et al., 2011) and which physical nature is still not yet fully understood (e.g., Liu et al., 2 MeteoSpace at Calern 2013; Warmuth, 2015). Both Ha flare ribbons and Moreton waves are chromospheric signatures of the coronal dynamics. The MeteoSpace instrument will operate in 2021 at Calern Their spatial and temporal evolution thus provide crucial infor- (OCA, 1270 m elevation, the sunniest station in France). It is mation on the flare/CME energetics (e.g., Gilbert et al., 2008; a fully automated system dedicated to short-term, high-cadence Veronig & Polanec, 2015), which can be used to estimate the monitoring of chromospheric activity. For that purpose, three potential impact of the flare/CME on the Earth’s magnetosphere telescopes will be available (Malherbe et al., 2019): two for in space weather forecast applications. Ha line and one for CaII K line. MeteoSpace will complete the world-wide Ha survey with 1.2 Long-term, low-cadence chromospheric enhanced features. It will join the GHN network, composed observations of many heterogeneous instruments in terms of cadence, spatial resolution, seeing, filter type and bandwidth. In terms of capa- On the other hand, long-term, low-cadence full-disk obser- bilities, MeteoSpace is close to the homogeneous GONG Ha vations of the chromosphere in CaII K and Ha lines, such as network (same filters), but it will offer improved temporal res- the centennial Kodaikanal (Hasan et al., 2010) and Meudon olution (15 s) and two Ha channels (line center and blue wing). collections (Malherbe & Dalmasse, 2019), are gold mines for MeteoSpace will also propose CaII K systematic images, with research on the solar cycle and its variability. The CaII K1v faster cadence (60 s) than previous routines (such as PSPT); imaging (blue wing) allows us to derive the sunspots number CaII K is more chromospheric than the space-borne SDO/AIA and area (e.g., Bertello et al., 2016; Chatterjee et al., 2016), 1600 and 1700 Å channels. while the Ha imaging enables us to compute the number of fil- The optical diameter of the three imagers is 100 mm with aments and their lengths (e.g., Mouradian & Soru-Escaut, 1993; 985 mm equivalent focal length. The filters bandwidth, optical Hao et al., 2015). All these quantities are good tracers of solar resolution on the Sun and observing cadence are given by activity that permit us to probe the properties of the solar cycle Table 1.

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